Polarization-entangled photon pairs using spontaneous four-wave mixing in a fiber loop

We generate polarization-entangled photon pairs in the 1550-nm wavelength telecom band, using spontaneous four-wave mixing in a highly nonlinear fiber loop. With accidental coincidences subtracted, we obtain coincidence fringes with visibilities greater than 86%, and thus observe a violation of Clauser, Horne, Shimony and Holt (CHSH) inequality by 2.7 standard deviations. The experimental setup is built using only fiber connections, which contribute to its long time stability.